1. Field of the Invention
The present invention relates to a failure diagnostic device for diagnosing whether a failure has occurred in an acceleration sensor, an electronic device equipped with the failure diagnostic device, a failure diagnostic system, and a failure diagnostic method.
2. Description of the Related Art
An acceleration sensor is loaded in electronic devices of various types. An output from the acceleration sensor is widely used for control of the electronic devices, detection of phenomena such as earthquake behavior or exercise intensity of a living body, and so on.
In the case where the acceleration sensor is loaded specifically in a portable electronic device, a large impact may likely be applied to the electronic device, if the electronic device is inadvertently dropped, for instance. After the impact over a rated value is applied to the acceleration sensor loaded in the electronic device, the acceleration sensor may cause an output value error, which may obstruct output of a normal output value.
If a user of the electronic device is kept being uninformed of abnormality of the acceleration sensor despite of the sensor abnormality, measurement or a like operation is performed under a condition that the user is unaware of the sensor abnormality. As a result, it may be unavoidable that erroneous control or erroneous phenomena detection is carried out by the electronic device based on the erroneous measurement data.
Japanese Unexamined Patent Publication No. 11-211751 discloses an acceleration detecting device, as a technology relating to failure detection of an acceleration sensor. The acceleration detecting device includes a pair of acceleration sensors, and is so constructed that sensitivity axes of the respective acceleration sensors are inclined relative to a horizontal axis, and outputs i.e. vectors from the respective acceleration sensors are distributed in a horizontal direction and a vertical direction in accordance with the inclined angles of the sensitivity axes. The sum i.e. a composite vector of the outputs from the respective acceleration sensors in the horizontal direction is calculated as a horizontal acceleration, and the sum of the outputs from the respective acceleration sensors in the vertical direction is calculated as a vertical acceleration. The acceleration detecting device detects whether a failure has occurred in the acceleration sensors based on the horizontal acceleration and the vertical acceleration. The publication discloses providing a computation circuit including amplifiers and adders of realizing computations corresponding to the vector distribution and the vector synthesis so as to obtain the horizontal acceleration and the vertical acceleration.
There is also known use of a reference sensor for detecting a failure of an acceleration sensor, in addition to the above publication.
The arrangement disclosed in the publication has the two acceleration sensors to judge whether a failure has occurred in the acceleration sensors, which increases the cost and the size of the acceleration detecting device. Also, the latter technology of using the reference sensor to detect whether a failure has occurred in the acceleration sensor needs another sensor i.e. the reference sensor in addition to the acceleration sensor for failure detection. Therefore, the latter technology has room for improvement on cost reduction and miniaturization of the acceleration detecting device, as well as the arrangement disclosed in the publication.